Only want user to put in one value

Here's the situation: 


I have a module with two Boolean line items that should act as the inverse of each other. As an end user, I should not be able to click both boxes. Screenshot below 




Basically, If the user picks the home team to win they should not be able to choose the Away Team to Win.
I thought IF Home Team to Win? = TRUE ELSE FALSE would work but I continue to get this error. 



Best Answer